1. Field of the Invention
The present invention relates to a technology that is well adaptable to an electric storage device in which ions are doped into at least one of a positive electrode and a negative electrode.
2. Description of the Related Art
A high energy density or high output density is demanded for an electric storage device that is mounted to an electric vehicle, hybrid vehicle, or the like. Therefore, a lithium ion battery, hybrid capacitor, or the like have been proposed as a candidate for the electric storage device. Particularly, the lithium ion battery that employs vanadium oxide for the positive electrode is excellent in taking lithium ions therein. Accordingly, the lithium ion battery can remarkably increase an energy density.
There has been proposed that lithium ions are doped beforehand into a carbon material for a negative electrode, included in the lithium ion battery, so as to decrease a potential of the negative electrode, whereby an energy density is increased. In order to dope lithium ions into the negative electrode, a method of bringing a negative electrode and a metal lithium, which are opposite to each other, into an electrochemical contact has mostly been employed. Another proposal has been made in which through holes in which lithium ions pass are formed on a positive-electrode current collector or a negative-electrode current collector in order to smoothly move the lithium ions between the laminated electrodes (e.g., see International Publication 04/59672).
In the electric storage device disclosed in International Publication No. 04/59672, lithium ions can be smoothly doped. However, this device is configured to dope lithium ions into only a negative electrode, thereby entailing a problem that the doping time can be increased at the last stage when the doping capacity of the negative electrode is decreased. The increase in the doping time as described above entails not only the degradation in productivity of an electric storage device but also the increase in cost of an electric storage device.